Heat recovery



D. K. DEAN HEAT RECOVERY Jan. 17, 1933.

2 Sheets-Sheet 1 Filed NOV. 1, 1928 INVENTOR fl/ow K054 2. BY ATTORNZ Jan. 17, 1933. D, DEAN 1,894,758

HEAT RECOVERY Filed Nov. 1, 1928 2 Sheets-Shet 2 TOR 5/0 054 ATTOREY i as it is of appreciable amount.

liquor. The liquor Patented 17,

UNITED STATES PATENT. OFFICE DION K. DEAN, 0F BAHWAY, NEW JERSEY, 'ASSIGNOR TO FOSTER WHEELER CORPORA- TION, YORK, N. Y A CORPORATION OF NEW YORK HEAT RECOVERY Application filed November 1, 1928. Serial No. 316,499.

My invention relates to heat recovery and has for its principal object to recover the waste heat in liquor discharged from a pulp digester. In a number of processes, particularly in connection with paper mills in which old paper stock is de-inked, the paper stock 18 heated to a high temperature in a relatively large amount of water and is digested for a considerable period at the high temperature. When the digesting is over, it is customary to conduct the pulp to the next stage in the process and dissipate the heat of the pulp liquor. I propose to make-use of this heat In my method of recovering the heat I propose to use the principle or" flashing steam by lowering the pressure of hot water. The steam thus produced is pure and can be used in a number of ways. I prefer to use it for heating fresh water and I accomplish this in a multi-stage evaporator system.

My invention will be further explained by reference to the accompanying drawings showing parts of a. plant for carrying out the invention and whereon:

Fig. 1 shows one arrangement of apparatus for carrying out the invention;

Fig. 2 is a side View of the arrangement shown in Fig.1; and

Fig. 3 is a view at right angles to Fig. 2 showing a loop in a connection between condensers.

Reference character 10 designates a digester for digesting pulp. It may be a sulphite or sulphate or old paper stock digester. After a cook the digester'dischar es pulp discharged maylie waste liquor, the pulp being separated or it may contain the pulp. The pulp liquor is conducted through conduit 11 to first stage evaporator 12. The evaporator may be of any various known types ofoonstruction. This evaporator is maintained at a low absolute pressure, for example, about 5 inches of mercury absolute. This'low absolute pressure of vacuum is maintained by first stage condenser 13 connected to the evaporator by conduit 14. Vacuum pump 15 withdraws gash-0m condenser 13 and tail pump 16 withdraws condensate.

The temperature of the pulp liquor entering first stage evaporator 12 will have a temperature of, let us say, 170 F. In view of the low pressure, some of the water of the liquor flashes into steam. As steam is formed the temperature drops in order to supply the latent heat of evaporation until a liquor temperature is reached which correspondsto the pressure of about 5 inches of mercury, which is about 135 F. The flash steam formed in this stage passes through conduit 14 and is condensed in condenser 13. In condensing it gives up heat to and heats fresh water supplied to condenser. 13 through conduit 17. The water heated and the steam to be condensed are in direct contact in condenser 13 and the resultant hot water passes out through conduit 18 and is forced by ump 16 to the point of use which may be a di erent digester about to be heated.

About 5% of the water of the pulp liquor is evaporated in evaporator 12. The remaining pulp liquor passes through pipe 19, which is arranged to provide a sealing loo and into second stage evaporator 20. econd stage evaporator 20 is at a lower level than first stage evaporator 12 to permit the liquor to flow by gravity from the latter to the former.

In the second stage evaporator 20, a still lower pressure is maintained, let us say 1.5 inches of mercury absolute. The corresponding boiling point of water is about 90 F. The liquor entering the second stage evaporator 20 has a temperature of about 135 F., de termined by the pressure in first stage evaporator 12. Consequently, the temperature being above the boiling point, steam flashes in the second stage evaporator, the temperature lowering to or toward 90 F.

Evaporator 20 is equipped with a cone bafile 30 for distributing the liquor. Evaporator 12 .is preferably equipped with a similar bafliel The steam formed in evaporator 20- passes through conduit 21 and into second stage condenser 22; Condenser. 22 receives the fresh water to be heated through inlet 23.

17 and into first stage condenser 13 where it is further heated, as above explained due to the higher temperature of steam supplied to condenser 13.

The lower pressure in second stage evaporator 20 p is maintained by condenser 22. Condenser 22 can produce a lower pressure because the temperature of cooling water is lower in condenser 22 than in condenser 13. Non-condensable gas, together with some steam, is withdrawn from condenser 22 by pump 24 and passes into condenser 13 through conduits 25 and 14. Pumps 15' and 24 are preferably steam jet pumps supplied with steam from any suitable source. The steam supplied to pump 24 is condensed in condenser 13. The steam supplied to pump 15 is condensed in an after-condenser 26 through which the hot water discharged by pump 16 passes. The heat of the steam used to operate pumps 15 and 24 is thus completely recovered.

The height of condenser 22 above condenser 13 and consequently the unbalanced liquid column in'pipe 17 serves to permit the higher pressure in condenser 13 than in condenser 22. The arrangement also facilitates flow-by gravity from condenser 22 to condenser 13.

The loop in pipe 19 should be sufiiciently lon or have sufficient resistance so that the hig er ressure in evaporator 12 will not empty t e loop but maintain a seal permitting the difl'erent pressures to exist in the evaporators.

The liquor leaves evaporator 20 through pi i i128and pump 29.

e measure of heat recovery is the quantipump 16 multity of water passing through plied by the difference in temperature tween t e supply water.

It will be understood that the values of temperature and pressure given are for illustrative purposes only. These are approximately the temperatures and pressures existing inone plant equipped with the present invention. 3

While I have shown the invention as applied to the heating of fresh water, it will be understood that the flash steam may be used to-heat other fluids or substances. F urthermore, while I have illustrated and described a two stage evaporator system it will be obvious that one or three or more stage or stages may be used. Essentially, what I-have provided in the described embodiment is a plurality of evaporators arrangedin series in each of which steam is flashed and a plurality of water heaters arranged in series throng which a stream of fresh water flows and crossconnections conducting the flashed steam into the 'water heaters in inverse relation to flow; that is, so that the steam firstflashed goes to the last water heater in line of flow, I do not resultant hot water and the cold mamas limit myself to any specific type of evaporator or condenser. i

It will be seen that my process of heat recovery is continuous.

What I claim .is:.

1. The process of recovering heat from hot pulp liquor discharged from a digester which comprises successively lowering the pressure and the temperature of the hot pulp liquor and flashing steam therefrom at difierent temperatures, and producing flow of and progressively increasing the temperature and the pressure of water in direct contact with the flashed steam of different temperatures.

2. The process of recovering heat from hot liquid carrying material in suspension which comprises successively lowering the pressure and the temperature of the liquid-and flashing steam therefrom at different temperatures, conducting water in direct contact with the flashed steam of diiferent temperatures and progressively increasing the temperature and the pressure of the water.

3; The process of recovering heat from hot pulp liquor discharged from a digester which comprises successively lowering the pressure and the temperature'of the hot pulp liquor and flashing steam therefrom at different temperatures, producing flow of and progressively increasing the temperature and the pressure of water in direct contact with the flashed steam of different temperatures, balancing the pressure drop in the .pulp liquor a hydrostatic column and utilizing a hydrostatic column to produce the rise in pressure of the water. i

4. The' process of recovering heat from liquid carrying material in suspension which comprises successively lowering the pressure and the temperatureof the liquid and flash ing steam therefrom at different temperatures, producing flow of and progressively increasing the temperature and the pressure of fresh water in direct contact with the flashed steam of different temperatures, balancing the pressure drop in the liquid having material in suspension by a hydrostatic column and utilizing a second hydrostatic column to produce the rise in pressure of the fresh water.

5. Apparatus of the character set forth for treating pulp liquor and the like comprising a first evaporator, a second evaporator, a first condenser, a second condenser, "a vapor connection between the first evaporator and the first condenser, a vapor connection between the second. evaporator and the second condenser, means for conducting liquid from'the first evaporator to the second evaporator and liquid from the second condenser to the first condenser and for maintaining a higher pressure in the first evaporator and first condenser than in the second evaporator and second condenser comprising a connecting contreating pulp liquor and the like comprising treating pulp liquor and the like comprising a first evaporator, a second evaporator, a first condenser, asecond condenser, a vapor connection between the first evaporator and the first condenser, a vapor connection between the second evaporator and the second condenser, means for conducting liquid from the first evaporator to the second evaporator and liquid from the second condenser to the first condenser and for maintaining a higher pressure in the first evaporator and first condenser than in; the second evaporator and second condenser comprising an unrestricted relatively large connecting conduit between the first evaporator and the second evaporator adapted to hold a hydrostatic column of liquid and a connecting conduit'between the second condenser and the first condenser adapted to hold a hydrostatic column of liquid, means to supply liquor to be treated to the first evaporator, means to withdraw treated liquor from the second evaporator,

means to supply cold water to the second condenser and means to withdraw water from the first condenser. y

7. Apparatus of the character set forth for treating pulpj liquor and the like comprising a first evaporator, a second evaporator, a first condenser, a second condenser, a vapor connection between the first evaporator and the first condenser, a vapor connection between the second evaporator and the .second condenser, means for conducting liquid from the first evaporator. to the second eva orator and 1i uid from the second con enser to the st condenser and for maintaining a higher pressure in the first evaporator and first condenser than in the second evaporator and second condenser comconduit evapof liquid and a connecting conduit between the second condenser and the first condenser adapted to hold a h drostatic column of liquid, means to supp y liquor to be treated to the first evaporator, means to withdraw treated liquor from the second evaporator, means to supply cold water to the second condenser andmeans to withdraw water from the first condenser. q

8. Apparatus of the character set forth for 'duit between the a first evaporator, a second evaporator, a first,

condenser, a second condenser, a vapor connection between the first evaporator and the first'condenser, a vapor connection between the second evaporator and the second condenser, means for conductin liquid from the first evaporator to the second evaporator and liquid from the second condenser to the first condenser and for maintaining a higher pressure in the first evaporator and first condenser than in the second evaporator and second condenser comprising a relatively large unrestricted connecting conduit forming a loop between the first evaporator and the second evaporator and adapted to hold a hydrostatic column of liquid and a connecting conduit between the second condenser and the first condenser adapted to hold a hydrostatic column of liquid, means to supply liquor to be treated to the first evaporator, means to withdraw treated liquor from the second evaporator, means to supply cold water to the second condenser and means to withdraw water from the first condenser.

9. The process of recovering heat from hot pulp liquor discharged from a digester which comprises successively lowering the pressure and the temperature of-the hot pulp liquor and flashing steam therefrom at different temperatures, producing flow of and progressively increasing the temperature and the pressure of water in direct contact with the flashed steam of different and balancing the pressure drop in the pulp liquor by a hydrostatic column.

10. Apparatus of the character set forth for treating pulp liquor and the like comprising a first evaporator, a second evaporator, a first condenser, a second condenser, a vapor connection between the first evaporator and the first condenser, a vapor connection between the second evaporator and the second condenser, means for conducting liquid from the first evaporator to the second evaporator and liquid from the second condenser to the first condenser and for. maintaining a higher pressure in the first evaporator and first condenser than in the second evaporator and second condenser comprising a connecting confirst evaporator and the second evaporator adapted to hold a hydrostatic column of liquid, means to supply liquor to be treated .to the first evaporator, means to withdraw treated liquor from the second evaporator, means to I su ply cold water to the second condenser, an means to withdraw water from the first condenser.

DION K- DEAN.

temperatures,- 

